The student was arrested after police searched his home and found the hit list and a plot to carry out a shooting at his school.

Argo and many others were wondering why the school didn't act and inform parents sooner.

"This wasn't just an idle threat, this kid wrote their names down and wrote down how he was going to kill them," Argo added.

Law enforcement said they were informed by a parent of a threat on social media on Saturday, but the post may have been up since last Thursday.

The school was notified and the student accused of making the threats was kept at home, investigators said.

"There certainly was potential, in this case, for harm. He had the intent and capability, based on what we know today, to carry out an attack at that school," said San Bernardino Sheriff John McMahon in a press conference on Wednesday.

Argo added the student had been troubled for some time.

"This kid has made a lot of comments to all these other kids about shooting up the school. My daughter mentioned to us last night the way he said hi to people was, 'Hey, go kill yourself,'" she said.

Many parents chose to keep their kids at home on Thursday, and others who took them to school did so reluctantly.

"Please be careful. You know, with everything that's gone on from Columbine, you know, the movie theater, all this stuff, that's really scary," cried mother Claudia Gallardo.